Following code executes without NPE being thrown:

import java.util.Arrays;

public class Test {
    public static void main(String[] args) {
        Arrays.parallelPrefix(new double[0], null);
        Arrays.parallelPrefix(new int[0], null);
        Arrays.parallelPrefix(new long[0], null);
        Arrays.parallelPrefix(new Object[0], null);

        Arrays.parallelPrefix(new double[0], 0, 0, null);
        Arrays.parallelPrefix(new int[0], 0, 0, null);
        Arrays.parallelPrefix(new long[0], 0, 0, null);
        Arrays.parallelPrefix(new Object[0], 0, 0, null);
    }
}


However according to spec NPE should be thrown - all the methods contain following:

* @throws NullPointerException if the specified array or function is null

It's understandable that why this happens but anyway behavior should correspond to spec.

The minimized test is attached.